Fish oil, supplements to ease menopausal symptoms, and breast cancer risk

July 8, 2010

Fish oil supplement use was associated with a decrease in the risk of breast cancer, while supplements used to ease menopausal symptoms had no impact on risk, according to results from the Specialty Supplements and Breast Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort Study, published this week in Cancer Epidemiology, Biomarkers & Prevention.  Over 35,000 postmenopausal women aged 50-76 years completed a 24-page survey of their supplement use in 2000 to 2002, and by 2007, 880 women had developed breast cancer.  A statistical analysis was done to determine if any supplements were associated with the risk of developing breast cancer.  Only the current use of fish oil was associated with a decrease in the risk of breast cancer, while no association was found with the use of black cohosh, dong quai, soy, or St. John's Wart.  The association between fish oil use and a decrease in breast cancer risk held up after taking into account age, BMI, alcohol consumption, fruit and vegetable consumption, family history of breast cancer, and aspirin use.  The association only applied to ductal carcinoma, not lobular, and for localized breast cancer, but not metastatic. 

The investigators suggest that the association may be explained by fish oil's possible anti-inflammatory effects.  Chronic inflammation has been linked to factors associated with cancer initiation and progression.  However, they caution that this is an observational study and that fish oil use must be evaluated in a randomized clinical trial before it should be promoted for the reduction of breast cancer risk.  Previous links between dietary supplements and cancer risk found in observational studies have not held up after investigation in randomized, clinical trials.